1. Field of the Invention
This invention relates to improvements in effecting chemical reactions, and more particularly, to an improved method and apparatus especially effective in carrying out wet oxidation of waste streams including sewage sludge.
2. Description of the Prior Art
Above ground wet oxidation systems have been in use for several years with limited success for the destruction of municipal sludge received from a sewage treatment process. The above-ground wet oxidation systems use high surface pressure and heat to initiate the wet oxidation reaction, however, the apparatus is not energy efficient, the system is subject to failure and results in only partial oxidation of the sludge; see, for example, U.S. Pat. No. 2,665,249 of Zimmermann and U.S. Pat. No. 2,932,613 of Huesler et al. The above ground wet oxidation processes have not, therefore, replaced the traditional methods of treating municipal sludge, which includes settling, dewatering, drying, incineration and the like.
Various vertical or down-hole fluid treatment systems have been proposed by the prior art but are used only in very limited applications. A down-hole fluid treatment system utilizes vertical pipes which generally extend downwardly into the ground from a control station. The fluid to be treated is pumped into the vertical reactor pipes and the fluid head creates a pressure which assists in the desired fluid process or reaction. In the processes used to date, the reaction requires additional heat which may be added by electrical resistance coils or heated fluid which circulates in a heat exchanger. Air or other gases may be added to the fluid being treated to assist in the reaction.
Although several prior art patents propose a vertical well wet oxidation reaction system for treatment of municipal sludge or other fluid waste streams, the processes and apparatus disclosed in these patents have not been successful; see, for example, U.S. Pat. No. 3,449,247. As recognized by these prior art patents, the pressure created by the fluid head is dependent upon the length of the reactor. Thus, it is theoretically possible to fully oxidize municipal sludge at a depth of approximately one mile provided the concentration of the oxidizable material in the municipal sludge is balanced against the oxygen available in the air injected into the system. To applicants' knowledge, however, no one has been successful in building a down-hole wet oxidation system for municipal sludge except the Assignee of the present invention.
U.S. Pat. No. 4,272,383 of McGrew, assigned to the Assignee of the present invention, discloses the principles of the first successful down-hole wet oxidation reaction system for municipal sludge. The apparatus disclosed in the McGrew patent includes a series of generally concentric nested pipes or tubes wherein dilute organic waste is preferably received in the inner pipe and flows downwardly to a reaction zone adjacent the bottom of the pipe and recirculated upwardly through a second pipe, which surrounds the inner pipe, following the reaction. Compressed air or oxygen is injected into the downwardly flowing sludge preferably forming Taylor-type gas bubbles. In the McGrew patent, the temperature of the reaction is controlled by a heat exchanger jacket which surrounds the inner concentric pipes wherein heated oil or other heat exchange fluid is pumped into the jacket to control the temperature of the reaction zone.
The treatment apparatus of this invention provides a method and apparatus for effecting chemical reactions characterized by minimum initial capital costs, a relatively high overall thermodynamic efficency, excellent containment and durability, and an overall simplicity of construction and operation with a minimum space requirement. Moreover, the present invention provides a novel ground surface method and apparatus for enhancing chemical reactions at high temperatures and pressures without the necessity of the customary large pressure vessels that require constant mechanical stirring and considerable land surface area. Further, the present invention solves a number of environmental, excessive energy, and maintenance problems presently associated with handling waste above ground.